WEAPONS are pouring into the Balkans despite an arms embargo, which the international community doggedly maintains in the belief that it will prevent the Bosnian war from spreading to other flashpoints in the region.

Some of the weapons are paid for by wealthy expatriates in North America and Australia. Others are bankrolled with the profits of the heroin trade to Western Europe. More often, sympathetic governments, including Iran, fund the purchase of arms.

Some heavy weapons get through the Nato screen to the Balkans, but the trafficking is mostly in machine-guns, automatic rifles, mortars, grenades and explosives.

As in most of the 30 present conflicts in the world, light weapons are the cause of most military and civilian casualties, according to Aaron Karp, an expert in the way weapons reach insurgent groups. He calculates that it costs about dollars 75m ( pounds 51m) a year to equip a militia army of 10,000 troops with light arms.

Serbia is almost immune to the arms embargo and, says Jane's Defence Weekly, has completely reconstructed its formidable defence industry.

To get sophisticated equipment, such as the eight Hind helicopters the Bosnian army recently acquired, requires state sponsorship, arms experts say, in this case probably Iran. Another Bosnian arms deal linked to Iran surfaced with the seizure earlier this year of a Panamanian-flagged ship with surface-to-surface missiles, 25,000 machine-guns and 7 million rounds of ammunition. The previous year, after a CIA tipoff, an Iranian Boeing 747 at Zagreb airport was found to be carrying thousands of machine-guns and 40 Iranian volunteers.

The trend towards the use of drug profits to buy weapons for the Balkans - for present use or stockpiling for future conflicts - first came to light in 1991 when the Swiss police uncovered a large network of Albanians from the Serbian province of Kosovo buying semi- automatic weapons in Berne and Basle with proceeds of heroin sold in Switzerland.

Albanians now control up to 70 per cent of the Swiss heroin market and there are more than 2,000 Albanians from Kosovo in the country's jails on drugs- and arms-smuggling charges.

Bearing the brunt of Serbian aggression, and desperately poor, Kosovo's Albanian clans have turned to heroin smuggling to finance weapons deals, according to European police sources. Recently eight Albanians, including a Macedonian deputy defence minister of Albanian origin, were arrested for smuggling arms into Macedonia, sparking fears of the Bosnian war spreading.

Macedonia's Foreign Minister, Ljubomir Frekovski, has described four channels through which arms flow - two routes across Bulgaria for weapons bound for Bosnia and Croatia, one through Thessaloniki in Greece and another through Albania.

'It is easier to buy a modern machine-gun in the Balkans today than a Toblerone chocolate bar,' one expert noted.

Despite the three-year-old arms embargo on all six republics of the former Yugoslavia, arms - even large weapons such as tanks, fighter planes and helicopters - have made their way to Bosnia and Croatia from a variety of sources. These include East European arsenals, Islamic countries, the Italian Mafia and Russian mobsters.

Most of the arms flowing to the Balkans originate in the bulging inventories of the old Warsaw Pact. 'But by the time they arrive at their destinations they are usually covered with the fingerprints of criminals,' said Daniel Nelson of Old Dominion University in Norfolk Virginia, who has published a study of the arms trade to former Yugoslavia. He says Russian and other East European mafias are the middlemen in the trade.

Investigators in Florence, Italy, last summer began prosecuting 43 people on charges of smuggling weapons to and from East Europe, Belgium and former Yugoslavia. They point to the Mafia's growing links to criminal groups in arms-rich but cash-poor East European countries.

United Nations sources say the Bosnian army has taken delivery of at least eight former Warsaw Pact helicopters over the last six months. The helicopters, based in Zenica, are used to ferry arms, soldiers and the wounded.

By far the biggest beneficiary of the illict arms trade has been Croatia. Zagreb now boasts at least 16 Russian MI-17 utility helicopters that it did not possess before the war, and in the past few months, the HVO has suddenly started flying its own helicopter missions in western Herzegovina.

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